1. Field of the Invention
This invention relates in general to magnetic flux sensing apparatus and, in particular, to a magnetic head of the type employing a thin magnetic film structure as a magneto-resistive element responsive to the flux being sensed.
2. Background of the Invention
The use of a thin single domain magneto-resistive film in magnetic heads for field sensing purposes is known. Typically, an electrical sense current (either AC or DC) is passed through the magneto-resistive film while the film is exposed to a magnetic field. The magnetic field exerts a torque on the magnetic moment of the magneto-resistive film causing the resistance of the film to increase or decrease depending on the sense and magnitude of the field applied to the film. The resistance of the film is, therefore, the analog of the field strength.
One general type of thin-film magneto-resistive head known within the prior art is a yoke-type magnetic head, examples of which can be found in U.S. Pats. Nos. 4,150,408, 4,425,593 and 4,489,357. A yoke-type magnetic head is composed of a magnetically permeable yoke (typically NiFe) having two flux conducting limbs between which a transducer gap is formed. One of the limbs (limb #1) of the magnetically permeable yoke is interrupted by a space that is bridged by a magneto-resistive element. The magneto-resistive element must, of course, be electrically insulated from the magnetic as well as from electrically conductive parts of the yoke structure. The electrical insulation may be provided by a layer of silicon dioxide (SiO.sub.2).
It will be appreciated that in order to maximize the sensitivity of the yoke-type magnetic head, it is necessary to optimize the coupling of the magnetic flux from the flux conducting limb (limb #1) of the permeable yoke to the magneto-resistive element and back to such limb of the yoke. The coupling of signal flux can be increased by reducing the thickness of the SiO.sub.2 layer that electrically insulates the magneto-resistive element from flux conducting limb #1. Reducing the insulating layer, however, increases the possibility of an electrical short circuit between the magneto-resistive element and the flux conducting limb #1 of the permeable yoke. Electrical noise in the output signal of the magneto-resistive element also increases as the insulating layer becomes thinner.
The insulating layer, while being a necessary element of the yoke-type head, unfortunately acts as a "flux barrier"--due to the high magnetic reluctance of the interface between the magneto-resistive element and the flux conducting limb #1--that prevents the yoke type head from achieving maximum sensitivity.